Method for increasing the tensile, breaking and flexural strength of colored leads and colored pencils containing the same

ABSTRACT

A method for increasing the tensile, breaking and flexural strength of coloured leads. The method is characterized in that 1 to 50 percent by weight alkyl and/or hydroxyalkyl cellulose which are soluble in organic solvents and whose alkyl radicals can be straight-chained or branched are added to the lead substance. The invention also relates to coloured pencils containing said coloured leads.

BACKGROUND OF THE INVENTION

The invention relates to a method of increasing the tensile strength,breaking strength and flexural strength of colored leads and to coloredpencils containing such leads.

Colored leads are leads containing pigments, color lakes or dyes, whichare used for colored pencils and cosmetics pencils. On the one hand,colored leads should be easy to apply, but must be solid enough toenable processing. Thus, when used in cosmetics pencils, for example,they should be able to be applied gently and softly to delicate areas ofskin and readily and intensively impart color upon application. For thisreason, they do not generally have a crystalline structure, but exhibitthixotropic behavior and desirably have only a low breaking strength.However, as result of this their tensile strength and flexural strengthis also low, which is disadvantageous. During shaping, the proportion ofwaste is high since the leads readily break when removed from the moldor when subjected to mechanical stress. Particularly in the case ofleads which have an unfavorable length to diameter ratio, for example adiameter of from 2 to 6 mm for a length up to 25 to 50 mm, the risk ofbreakage is high.

The low strength, in particular tensile strength and flexural strength,has proven particularly disadvantageous if thin colored leads having adiameter of less than 6 mm are to be inserted into a rotating pencilwhere, inserted into a rotary mechanism, they can be rotated out andback, but are not mechanically supported.

In the field of cosmetics pencils, so called “liners”—especially foreyeliner pencils and lipliner pencils, for example—which are suppliedinserted into rotary mechanisms, are popular. These liners do not haveto be sharpened and the lead, when it is not being used, is protected inthe liner sleeve.

Colored leads are usually produced by pouring a homogenized basic massbased on fat/wax mixtures, which, apart from the color-impartingpigments, may comprise further additives, into a mold, or extruding it.For use, the lead is either embedded in wood, poured into preshapedsleeves of wood or plastic or the like, or inserted into a rotarymechanism.

If casting molds are used, considerable forces of adhesion arise in thecooled mold, which, despite the use of release agents, readily leads totearing of the castings and thus to wastage. Moreover, extensivecleaning operations in the casting plant are required. The insertion ofthe colored leads into a rotary mechanism and the rotating out of theleads also frequently leads to breakage.

It is therefore an object of the invention to overcome the disadvantagesassociated hitherto with colored leads and to improve known pencilcompositions such that the tensile strength and flexural strength isincreased, such that even thin leads can be cast and extruded withoutremoval of the leads from the casting mold or insertion of the leadsinto a rotary mechanism leading to breakage or damage of the leads.However, at the same time the good and desired properties, in particularthe good application properties, of such leads should not be changeddetrimentally.

SUMMARY OF THE INVENTION

The foregoing object is achieved by providing, a method of increasingthe tensile strength, breaking strength and flexural strength of coloredleads which is characterized in that 1 to 50% by weight of alkyl- and/orhydroxyalkylcellulose whose alkyl radicals may be straight-chain orbranched and preferably have 2 to 10 carbon atoms, which is soluble inorganic solvents are added to the lead mass.

DETAILED DESCRIPTION

Surprisingly, it has been found that the addition of an alkyl- and/orhydroxyalkylcellulose, also referred to below as cellulose derivative,which is soluble in organic solvents gives the lead mass greaterelasticity without impairing the favorable properties of the lead andwithout detrimentally changing the properties of the other ingredients.

Although it was already known to use water-soluble cellulose derivativesas binders, in particular in the writing utensil industry, the additionof such water-soluble cellulose derivatives does not lead to an increasein the tensile strength and flexural strength of leads.

In addition, EP-A 0 861 657 describes cosmetic masses whose film-formingproperties and adhesion properties are said to be improved by theaddition of ethylcellulose. In particular, gel-like masses are to beprepared. However, this publication does not achieve the object on whichthe invention is based.

The basic mass for colored leads usually consists of fatty, wax and oilcrude substances. Additives may be added to this basic mass to achievedesired properties. The most important additives are coloring agents,which are added in the form of pigments, color lakes or dyes. Inaddition, binders and fillers are used to influence the consistency.Where appropriate, preservatives and antioxidants are added to improvethe durability and storability. A customary formulation for coloredleads comprises, for example, waxes, such as paraffin, beeswax etc., oilraw materials, such as hydrogenated vegetable oil, pigments forcoloring, and a solvent which is volatile at body temperature, such ascyclomethicones, which improve the ability of the lead to be appliedand, following application, evaporates to leave a durable colored line.The basic mass for the colored lead can, as desired and required,comprise further additives which are known to the person skilled in theart in this field and which require no further explanation here. Ifparaffin is used for the basic mass, its proportion should not be toohigh since excessive amounts of paraffin may lead to incompatibilitieswith the cellulose derivative used according to the invention.

According to the invention, a cellulose derivative, as defined below, isadded to a customary basic mass of this type for a colored pencil inorder to increase the tensile strength and flexural strength. Theproportion of the cellulose derivative can vary depending on the type ofbasic mass and the processing method. As a rule, a proportion in a rangefrom 1 to 50 parts by weight, based on 100 parts by weight of the basicmass, has proven favorable. An amount of less than 1 part by weight hasno significant effect on the strength, while if the proportion is morethan 50 parts by weight, the viscosity of the mass may be in a rangewhich is unfavorable for processing.

If the mass is to be extruded under high pressure, the proportion ofcellulose derivative may be in the upper range, whereas if the mass isto be shaped by casting, a proportion in the lower range is morefavorable. Preferably, not more than 30 parts by weight and particularlypreferably not more than 20 parts by weight of the cellulose derivativeare added. Particularly favorable results have been achieved with anaddition of from 3 to 10 parts by weight of cellulose derivative per 100parts by weight of lead basic mass.

A cellulose derivative used according to the invention is an alkyl-and/or hydroxyalkylcellulose soluble in organic solvents. To dissolvethe cellulose derivatives, organic solvents which can be used are, interalia, fatty alcohols, fatty acids and esters thereof. Alkyl- and/orhydroxyalkylcelluloses which are soluble in organic solvents areregarded, in particular, as those of which one part dissolves in up to100 parts of organic solvent at a temperature of 100° C.

Particular preference is given to using cellulose derivatives which aresoluble in fatty alcohols or fatty acid esters, in particular those ofwhich 1 g is dissolved in 1 to 100 g of the fatty alcohol, or ester at100° C.

The alkyl radical of the alkyl- and/or hydroxyalkylcelluloses may bestraight-chain or branched and has, for example, 1 to 10 carbon atoms.Preference is given to using cellulose derivatives whose alkylproportion has 2 to 6, in particular 2 or 3, carbon atoms, since theseare readily available. Particular preference is given to usingethylcellulose, optionally mixed with other cellulose derivatives.

The solubility of the cellulose derivatives depends, inter alia, ontheir degree of substitution. Preference is therefore given to thosecellulose derivatives whose degree of substitution is higher than 1.4.Particular preference is given to using ethylcellulose with a degree ofsubstitution of from 2.1 to 2.6 or a mixture of different derivativeswith a degree of substitution in this range.

Using the method according to the invention, it is possible to provide acolored lead whose tensile strength and flexural strength have beenimproved and which also has improved elasticity. It is stable enough tobe rotated out in a rotary mechanism without breakage and remainsself-supporting. The application properties are good, it being possible,for example, to apply it to skin in a pleasant manner.

Because of this improvement in the mechanical properties, leads can beprepared in which the length to diameter ratio may be greater than 5:1or 8:1 and even 10:1 and above.

The colored lead is prepared in a manner known per se by mixing andhomogenizing the components of the basic mass and the cellulosederivative used according to the invention and then shaping theresulting mass, usually by casting or extrusion, to give a lead.Usually, to prepare the leads, the mass is either poured into molds and,after cooling, removed from the molds, or is introduced into the holdingparts of a rotary mechanism, or poured directly into a suitable moldthrough a holding part and, after cooling, rotated back into the rotarymechanism, or else poured into a suitable section of a rotary mechanismand left to solidify there. Preferably, the colored lead according tothe invention is prepared by a casting process.

However, it has been found that cellulose derivatives soluble in organicsolvents cannot always be mixed with the basic mass for a colored leadwithout problems.

Preference is therefore given to using a method for the preparation ofcolored leads in which an alkylcellulose and/or hydroxyalkylcellulose,soluble in organic solvents, is dissolved in a cosmetically acceptablesolvent, the solution is mixed with the pencil mass and furtherprocessed in a manner known per se to give a lead.

The cellulose derivative used according to the invention is preferablydissolved in a solvent customary for the field of cosmetics. Preferenceis given to using a linear or branched fatty alcohol having a chainlength of from 7 to 50 carbon atoms, particularly preferably having 12to 34 carbon atoms and in particular 16 to 24 carbon atoms, a linear orbranched, saturated or unsaturated fatty acid, which preferably has achain length of from 12 to 24 carbon atoms, where the long-chain fattyacids are used particularly at elevated temperature, or an ester of afatty acid with a shorter-chain alcohol, in particular isopropylmyristate, isopropyl palmitate or myristic acid, optionally in a mixturewith fatty alcohols. It is also possible to use mixtures of theabove-mentioned alcohols and/or fatty acids and/or esters. Cetylalcohol, stearyl alcohol, isostearyl alcohol and behenyl alcohol, andmixtures thereof, have proven particularly suitable.

The cellulose derivative is dissolved in the solvent, optionally atelevated temperature, and then the basic mass is added. Since the basicmass is frequently homogenized at elevated temperature, it is preferableto likewise bring the solution comprising the cellulose derivative tothis elevated temperature prior to mixing.

The basic mass is mixed with the cellulose derivative and then furtherprocessed in a manner known per se, e.g. by extrusion or casting,preferably by casting.

In a preferred embodiment, the cellulose derivative is dissolved in acosmetically acceptable solvent, preferably a fatty alcohol, a fattyacid ester or an ester of a fatty acid and a fatty alcohol or a mixturethereof, the wax and fatty components are melted, the two are mixedtogether and homogenized, then, as coloring agents, pigments, colorlakes and/or dyes and optionally auxiliaries are added, and the basicmass is then poured into a mold and removed from the mold after cooling.

According to the invention, colored leads are obtained which can beprocessed without problems due to their improved strength propertiescompared with leads known hitherto. Since they break neither duringpreparation nor during use, they can be processed without problems togive pencils.

The invention thus also provides a colored pencil which comprises a leadand a sleeve, where the lead consists of a customary colored lead massto which 1 to 50% by weight of alkyl- and/or hydroxyalkylcellulose,soluble in organic solvents, have been added. The sleeve consists ofnatural or synthetic materials.

The colored leads obtained using the method according to the inventionare so stable that they can be processed by extrusion and casting and,furthermore, they have a sufficiently high flexural strength and tensilestrength for insertion into a rotary mechanism, and can be rotated inand out without breaking. They are likewise suitable to be introducedinto sleeve blanks and to be processed to give pencils.

The colored lead obtained according to the invention is preferably usedfor colored pencils and cosmetics pencils, particularly preferably forcosmetics pencils. Because of its advantageous properties, the coloredlead obtained according to the invention may be used for the preparationof eyeliner pencils, kohl pencils, eyebrow pencils and lipliner pencils.

Because of their increased tensile strength and flexural strength, theleads obtained according to the invention are particularly highlysuitable for use in cosmetic “liners” which have a rotary mechanism. Insuch pencils, the leads have a diameter of at most 6 mm, with a lengthof up to 80 mm. For this reason, the mechanical strength of such pencilsis subject to very high requirements; these are, however, met by thecolored leads obtained according to the invention.

The invention is illustrated using the examples below.

Example 1

Preparation of an eyeliner pencil

A colored pencil according to the invention was prepared using theformulation given in Table 1. For comparison, a lead was prepared fromthe identical basic mass, but which lacked the cellulose derivativesessential according to the invention. The formulation for the two massesis given in Table 1 below, all amounts being given in % by weight:

TABLE 1 INCI Name Example 1 Comparative Example 1 Colorants 33.30033.300 Ethylcellulose 1.500 — Isostearyl alcohol 5.900 5.900 Stearylalcohol 5.900 5.900 Hydrogenated vegetable oil 6.700 6.700 Paraffin6.700 6.700 Cyclomethicone 40.000 41.500 Total 100.000 100.000

For the lead of Example 1, the ethylcellulose was added to the mixtureof Isostearyl Alcohol and Stearyl Alcohol. The mixture was then heatedto 65 to 90° C. with stirring and maintained at this temperature untileverything had dissolved. Separately, Hydrogenated Vegetable Oil andParaffin were melted and then added to the ethylcellulose solution. Thepigments were then added and then the total mixture was homogenized in acustomary manner. Following the addition of Cyclomethicone, the mass waspoured into a mold in a known manner and, following cooling andsolidification, removed from the mold. This gave an eyeliner pencil withgood delivery, for soft application and good stability.

For comparison, the constituents of the formulation of ComparativeExample 1 were mixed in an equivalent manner by melting HydrogenatedVegetable oil and Paraffin and then adding the pigments and IsostearylAlcohol and Stearyl Alcohol. Finally, the Cyclomethicone was added tothe mass, and the mass was poured into a mold. A mass with comparabledelivery was obtained, but it did not have adequate breaking strength.This mass could therefore only be removed from the molds and rotatedback into the rotary mechanism with difficulty and with considerablewastage. During application, the leads with a diameter of 2.5 mm brokevery readily.

Example 2

Preparation of a lipliner pencil

A mass was prepared for a colored pencil which was suitable for alipliner pencil. For comparison, a lead for a lipliner pencil wasprepared whose basic mass was identical to that of Example 2, but whichlack ed the ethylcellulose essential according to the invention. Theformulations for both mixtures are given in Table 2 below in each casein % by weight.

TABLE 2 INCI Name Example 2 Comparative Example 2 Colorants 21.30021.300 Ethylcellulose 3.150 — Isostearyl alcohol 5.250 5.250 Cetylpalmitate 5.250 5.250 Beeswax 23.600 23.600 Synthetic wax 3.150 3.150PPG-12/SMDI Copolymer 1.600 1.600 Cyclomethicone 36.700 39.850 Total100.000 100.000

For the lead of Example 2, the ethylcellulose was added to a heatedmixture of Isostearyl Alcohol and Cetyl Palmitate, and then the mixturewas heated to 65 to 90° C. with stirring and maintained at thistemperature until everything had dissolved. Separately, beeswax,synthetic wax and PPG-12/SMDI Copolymer were melted and then added tothe ethylcellulose solution. The pigments were then added and then thetotal mixture was homogenized in a customary manner. Following theaddition of cyclomethicone, the mass was poured into a mold in a knownmanner and, following cooling and solidification, removed from the mold.This gave a lipliner pencil with good delivery, soft application andgood stability.

For comparison, the mass according to the formulation of ComparativeExample 2 was processed in an equivalent manner. For this, Beeswax,Synthetic Wax and PPG-12/SMDI Copolymer were melted and then pigments,Isostearyl Alcohol, Cetyl Palmitate were added and finallyCyclomethicone was added. The mass was then likewise poured into a moldin a manner known per se and, following cooling and solidification,removed from the mold. The lead obtained using the mass of ComparativeExample 2 had a comparable delivery, but had insufficient compressivestrength. It could only be removed from the molds and rotated back intothe rotary mechanism with difficulty and with considerable wastage.

The examples show that as a result of the addition according to theinvention of a cellulose derivative to a customary basic mass forcolored pencils, the mechanical properties, in particular the tensilestrength and flexural strength, and also the breaking strength, aregreatly improved without adversely affecting the advantageousapplication properties. The leads of the present invention are thereforeparticularly suitable for pencils with a rotary mechanism, where thelead is subjected to higher mechanical stress than in the case ofsharpenable, wood- and plastic-encased pencils. The colored leadsaccording to the invention are of course also suitable for wood- orplastic-encased pencils.

Example 3

Lead masses were prepared from Japan wax, Isostearyl Alcohol andEthylcellulose, without pigments, in order to test the mechanicalproperties of leads prepared therefrom. The weak point in the case ofthinly cast leads which are inserted into a rotary mechanism is thetransition point directly above the lead holder where the leads breakpreferentially. Masses were prepared with the compositions given below.Using this mass, leads with a diameter of 3 mm and a length of 34 mmwere cast and then subjected to various tests.

TABLE 1 2 3 Japan wax 50.000 50.000 50.000 (parts by weight) IsostearylAlcohol 25.000 25.000 25.000 (parts by weight) Ethylcellulose — 2.5005.000 (parts by weight)

3.a) Mold test

The resulting mass was poured into sleeve blanks then it was attemptedto remove the molding from the mold. Only the leads with formulation 3could be removed without problems and without auxiliary means, such asrelease agents, compressed air etc. In the case of the leads withformulation 2, considerable wastage arose. With the mass of formulation1, no leads could be removed from the molds.

3.b) Casting test

The masses with formulations 1, 2 and 3 were also tested in a rotarymechanism. For this purpose, a partially assembled mechanism was mountedon a metal mold and the mass in each case was then poured into the moldthrough the holding part. The following result was obtained:

Formulation 1. 20 break off out of 20

Formulation 2. 4 break off out of 20

Formulation 3. 0 break off out of 20

This shows that the lead mass obtained according to the invention hashigh stability and can be cast and removed from the mold withoutproblems.

3.c) Drop impact test

A drop impact test was carried out with the leads cast from the 3formulations. For this the complete mechanism with inserted lead wasdropped tip-first 3 times from a height of 30 cm in a guide tube onto ahard base. The result of the drop impact test was as follows:

Formulation 1. 20 break off out of 20

Formulation 2. 9 break off out of 20

Formulation 3. 0 break off out of 20

This test shows that the colored lead obtained according to theinvention which has excellent strength.

3.d) Tensile test

A tensile test was carried out using leads which had been prepared fromthe 3 formulations. For this purpose, a tensile force was exerted in theaxial direction onto a lead inserted into a rotary mechanism, and thevalue at which the lead broke off at the holding part was ascertained.The following results were obtained:

Formulation 1. 0.001 N to 0.005 N

Formulation 2. 0.020 N to 0.040 N

Formulation 3. 2.040 N to 3.400 N

This test shows that the colored lead obtained according to theinvention has excellent tensile strength.

3.e) Flexural test

A flexural test was carried out using the leads obtained from the 3formulations. For this purpose, the lead was in each case rotatedcompletely out of the rotary mechanism and then, from a distance of 34mm from the holding part, a force is allowed to act upon the lead. Thedeflection of the tip of the lead before it breaks off is measured. Thefollowing results were obtained:

Formulation 1. not able to be measured

Formulation 2. <1 mm

Formulation 3. 3 mm to 6 mm

This test shows that the colored leads obtained according to theinvention have excellent flexural strength.

The tests carried out demonstrate that it is possible according to theinvention to considerably increase the tensile strength and flexuralstrength even in the case of very thin leads, meaning that these can beused in rotary mechanisms without problems.

What is claimed is:
 1. A method for increasing the strength of anon-water based lead comprising: combining a non-water based lead massand an organic solvent with an additive comprising at least one of analkyl and a hydroxyalkylcellulose which is soluble in the organicsolvent, wherein the additive is present in an amount of between 1 to50% by weight and the alkyl radicals are one of straight-chain andbranch and have from 2 to 10 carbon atoms; and forming a lead from thenon-water based lead mass.
 2. The method as claimed in claim 1, whereinthe additive is present in an amount between 1 to 30% by weight.
 3. Themethod as claimed in claim 2, wherein the additive is present in anamount between 3 to 10% by weight.
 4. The method as claimed in claim 2,wherein the additive is ethylcellulose soluble in organic solvents isadded.
 5. The method as claimed in claim 1, wherein the organic solventis selected from at least one of a fatty alcohol and a fatty acid esterand wherein the additive is added in an amount of 1:1 and 1:100 withrespect to at least one of a fatty alcohol and a fatty acid ester at100° C.
 6. The method as claimed in claim 1, wherein the additive isdissolved in one of a fatty alcohol having a chain length of from 7 to50 carbon atoms and an ester of a fatty acid having a chain length offrom 12 to 24 carbon atoms.
 7. The method as claimed in claim 1, whereinin the organic solvent is selected from the group consisting ofisopropyl myristate, isopropyl palmitate, myristic acid, cetyl alcohol,stearyl alcohol, isostearyl alcohol, behenyl alcohol and mixturesthereof.
 8. The method as claimed in claim 1, including shaping acolored lead having a length to diameter ratio of at least 5:1.
 9. Themethod as claimed in claim 1, including shaping a colored lead having alength to diameter ratio of at least 8:1.
 10. The method as claimed inclaim 1, including shaping a cosmetic lead from the lead mass.
 11. Themethod as claimed in claim 1, including shaping a lead by casting.
 12. Acolored pencil comprising a non-water based colored lead and a sleeve,where the lead comprises from 1 to 50% by weight, based on the weight ofthe lead, of an additive comprising at least one of an alkyl and ahydroxyalkylcellulose having alkyl radicals which are one ofstraight-chain or branched and have from 1 to 10 carbon atoms, whereinthe additive is soluble in an organic solvent.
 13. The colored pencil asclaimed in claim 12, wherein the colored lead has a diameter of from 1to 6 mm.
 14. The colored pencil as claimed in claim 13, wherein thesleeve is equipped with a rotary mechanism, into which the colored leadis inserted.
 15. The colored pencil as claimed in claim 14, wherein thelead is self-supporting.
 16. A colored pencil comprising a colored leadhaving a diameter which is less than or equal to 6 mm and whose lengthis between 25 to 80 mm, wherein the lead is inserted into a rotarymechanism of a rotating pencil.
 17. The colored pencil as claimed inclaim 16, wherein the pencil is a cosmetics pencil.
 18. The coloredpencil as claimed in claim 17, wherein the cosmetics pencil is selectedfrom the group consisting of an eyebrow pencil, kohl pencil, eyelinerpencil and lipliner pencil.